During the last few years a series of chromosomal alterations associated with acute leukemia has been found in our laboratory to appear in a repetitive fashion in different and unrelated individuals. Initial investigations during this short period of time indicates that these aneuploid profiles may have a considerable clinical significance, particularly from a prognostic point of view. In addition, simultaneous ulstrastructural studies of samples of hematopoietic tissue obtained from these patients have demonstrated a specific nuclear alteration in the majority of the patients carrying aneuploid clones. The present proposal intends to continue and expand these sequential cytological studies of the leukemic patients in order to better characterize the phenomenon of aneuploidy in human leukemia and to more precisely identify the chromosomal elements involved in these aberrations. The chromosomal changes will be analyzed in greater detail than heretofore by the application of the new cytogenetic techniques (Quinacrine mustard fluorescence, Giemsa banding and heterochromatin staining). The true diagnostic and prognostic values of the aneuploid profiles that we have identified in acute leukemia will be determined. With the use of cytogenetic and ultrastructural markers it is intended to find out whether or not in the children, as well as in the adult, acute leukemia treated with HL-A bone marrow transplants, relapse represents either a recrudescence of the original process or a de novo leukemic transformation. Other technical procedures, such as the use of colony- forming capacity, cytofluorometric determinations and euchromatin ultrastructural probe (Frenster's technique), will be utilized to evaluate the leukemic bone marrows. It is anticipated that this combined approach will provide fundamental information regarding the biological behavior of the leukemic cell population. Application of this knowledge to the care of the leukemic patient should result in an improved clinical management and a more individualized and rational form of therapy.